The present invention is directed to a method for providing high flux, thin film composite membranes on a microporous hydrophobic support.
The use of membranes to separate aromatics from saturates has long been pursued by the scientific and industrial community and is the subject of numerous patents.
U.S. Pat. No. 3,370,102 describes a general process for separating a feed into a permeate stream and a retentate stream and utilizes a sweep liquid to remove the permeate from the face of the membrane to thereby maintain the concentration gradient driving force. The process can be used to separate a wide variety of mixtures including various petroleum fractions, naphthas, oils, hydrocarbon mixtures. Expressly recited is the separation of aromatics from kerosene.
U.S. Pat. No. 2,958,656 teaches the separation of hydrocarbons by type, i.e. aromatic, unsaturated, saturated, by permeating a portion of the mixture through a non-porous cellulose ether membrane and removing permeate from the permeate side of the membrane using a sweep gas or liquid. Feeds include hydrocarbon mixtures, naphtha (including virgin naphtha, naphtha from thermal or catalytic cracking, etc.).
U.S. Pat. No. 2,930,754 teaches a method for separating hydrocarbons e.g. aromatic and/or olefins from gasoline boiling range mixtures, by the selective permeation of the aromatic through certain cellulose ester non-porous membranes. The permeated hydrocarbons are continuously removed from the permeate zone using a sweep gas or liquid.
U.S. Pat. No. 4,115,465 teaches the use of polyurethane membranes to selectively separate aromatics from saturates via pervaporation.
U.S. Pat. No. 4,837,054 teaches thin film composite membranes prepared by deposition from a solution. A thin film of polyurea/urethane is coated onto a microporous support substrate from a multi-component solvent system. The solution of polyurea/urethane copolymer is prepared in a solution system consisting of an aprotic solvent such as dimethylformamide, a cyclic ether such as dioxane, a third component comprising cellosolve acetate or methyl cellosolve and a wetting agent such as crotyl alcohol. The polymer in the solvent solution is deposited as a thin film on a support substrate such as polyethylene, polypropylene or teflon after which excess polymer/solvent solution is permitted to drain from the support. Thereafter the solvents are permitted to evaporate leaving a thin layer of active polyurea/urethane copolymer on the support backing. The solvent system employed constitutes a mixture of (a) an aprotic solvent such as DMF, (b) a cyclic ether such as dioxane, (c) cellosolve acetate or methyl cellosolve, and (d) a wetting agent such as crotyl alcohol. These solvents are used in a parts per hundred ratio of a/b/c/d in the range about 3-27/94-33/2-33/1-7. The polyurea/urethane copolymer exists as a true, complete copolymer in the solvent system and the polymer-solvent system exists as a true solution. The polymer concentration in the solution can range up to 40 parts polymer per 100 parts solvent, preferably 0.5 to about 20 parts polymer, more preferably 1 to 10 parts polymer, most preferably 1 to 5 parts polymer per 100 parts solvent solution.